Method and apparatus for controlling suspension concentrations



April 22, 1969 G. MATKOVICH 3,440,160

METHOD AND APPARATUS FOR CCNTROLLING SUSPENSION CONCENTRATIONS Filed Feb. 9, 1966 Way United States Patent 3,440,160 METHOD AND APPARATUS FOR CONTROLLING SUSPENSION CONCENTRATIONS George Matlrovich, Stamford, COl'llL, assignor to lPitney-Bowes, lnc., Stamford, Conn., a corporation of Delaware Filed Feb. 9, 1966, Ser. No. 526,244 lint. Cl. B01k 5/00 US. Cl. 204-180 5 Claims ABSTRACT OF THE DISCLOSURE Excess toner particles in the liquid of an electrostatic developer tank are plated on charged electrodes and released as desired by DC. current control.

This invention relates to a novel method and apparatus for varying the concentration of toner particles in a suspension. More particularly, the invention relates to a novel method and apparatus for varying the concentration of charged toner particles that are suspended in a dielectric fluid.

In the operation of electrofax type photocopy machines having liquid toner developing means, the efiective concentration of toner particles in the developer bath gradually decreases as exposed copy sheets are successively fed through said bath. After an extended period of use the concentration of said toner particles is reduced to a level such that the visible print on the developed sheets is too light for easy reading. At this point the customary practice is to add more toner particles to the liquid developer bath. When this is done however a concentration of toner particles may result which is above a desired level in which case an initial subsequent period of machine operation must be tolerated where the copy work is poor because of excess and/or random deposition of toner particles in the image and non-image areas of the copy sheet. This undesirable type of performance will continue until the toner concentration has dropped to the desired level. The instant invention contemplates the elimination of such an initial period of machine operation.

The primary object of the instant invention is to provide a novel method and apparatus for controllably reducing at any time the concentration of toner particles in the liquid developer bath of an electrofax type photocopy machine.

Another object of the instant invention is to provide a chargeable plate means in the liquid developer bath of an electrostatic type photocopy machine whereby a strong electrostatic field may be applied to said bath.

Other objects will become apparent as the disclosure progresses.

In the drawings:

FIG. 1 is a sketch illustrating the structural environment of the instant invention.

FIG. 2 is a cross sectional view of the liquid toner developer tank and shows the arrangement of electrostatic field producing means for controlling the toner particle concentration in the developer bath.

Referring to FIG. 1 there is diagrammatically shown a portion of an electrostatic photocopy machine having a base 11 and a pair of spaced side frames 12 rigidly mounted thereon. This type of machine includes a suitable copy sheet roller transport means 13, a charging means 14- for imposing a high electrostatic charge on a photoconductive type copy sheet, and an exposure station 15 at which the charged copy sheet is subjected to a light image 16. The machine is also provided with a developing means 17 which in this particular case comprises a liquid toner bath. In FIG. 1 the path of move- 3,440,160 Patented Apr. 22, 1969 "ice ment of the copy sheet through said portion 10 of the machine is denoted by the dot-dash line arrow 20. The general construction and operation of the above described type of machine is well understood in the art and need not be further discussed here.

Of primary concern here is the characteristic of operation of the liquid toner developer means 17. Referring to FIGS. 1 and 2 there is shown a plastic or other nonconductive toner tank 21 which is suitably mounted on the machine base 11 and which is disposed between the side frames 12. The tank 21 is generally rectangular in shape and is provided with a plurality of conventional type guide rods or the like 22 which are suitably supported at the upper edges of the tank and which effectively define the path of movement of the copy sheet through the liquid toner bath. The tank 21 contains a liquid mixture or bath or reservoir 23 comprising a dielectric fluid, such as kerosene, with printing toner particles suspended therein. An inverted concentrate supply bottle 24 is mounted on the adjacent side frame 12 by means of a suitable bracket 25, the lower open end 26 of the bottle serving to keep the developer bath at an operative level 27. The bottle 24 contains a toner replenishing concentrate that includes an additional amount of said dielectric liquid having a relatively large quantity of printing toner particles suspended therein, the toner particles concentration here being very high relative to that of said bath 23. As is well known in the art the usual toner particles employed in the developer bath have an inherent positive charge which is acquired during the grinding or other operations of the toner manufacture. Any suitable bath stirring means may be used here as is diagrammatically illustrated at 28, FIG. 2 in order to properly maintain the toner suspension in the bath 23.

During operation of the instant type of photocopy machine the developer bath 23 will be progressively depleted and the fluid level in the tank will drop below the said level 27 of the lower end 26 of the supply bottle 24 whereupon the bath will be automatically replenished by a flow of concentrate from the supply bottle into bath 23 until the fluid level again reaches said level 27. Thus the bath 23 is automatically restored to the desired level 27 and a replenishing supply of printing toner particles is simultaneously added to the developer bath. After completion of such replenishment of the developer bath it may turn out that too much toner has been added, i.e. the concentration of toner particles in the bath 23 has become too high. In this case there has heretofore been no way of readily decreasing such a high toner concentration and thus there would be a subsequent period of machine operation where the excess toner particles would cause smudged backgrounds, swirl and other improper characteristics in the copy print work.

The instant invention provides a method and apparatus whereby the concentration of toner particles in the developer bath may be reduced in those cases where a bath replenishment operation produces too high a toner concentration. Referring to FIG. 2 a pair of metal electrode plates 30, 31 are suitably supported in the plastic tank 21, said plates being respectively connected through wires 32, 33 to the two output terminals of a high voltage electrical power supply unit 34 that is suitably mounted on the side frame 12 of the machine. A normally off switch 35 is connected between said power supply 34 and an electrical supply source. With this plate arrangement whenever the concentration of toner particles in the developer bath is too high, as determined by visual inspection of the copies then being produced by the machine, the switch 35 is turned to its on condition so that a high voltage is applied to the plates 30, 31. The high positive and negative charges respectively existing on said plates will thus set up a strong electrostatic field in the developer bath 23 and the positively charged toner particles will migrate toward and deposit out on the negative electrode plate 31. The electrodeposition of toner particles on plate 31 will reduce the toner particle concentration of the developer bath and is continued until visual inspection of the print work produced by the machine indicates a proper toner particle concentration for developer bath. The switch 35 is then returned to its 011 condition so that said electrodeposition of toner particles onto plate 31 will terminate, the liquid developing bath then being conditioned for an extended period of developing proper print work on successive copy sheets. When the liquid level in tank 21 again becomes lower than said level 27 another toner replenishing operation is automatically completed and if there is a resultant unacceptably high concentration of toner particles in the bath another electrodeposition operation may be carried out as above described to again reduce said concentration to an acceptable level.

This above described technique for toner concentration control improves the ability to obtain consistently good print work from a liquid toner type electrostatic photocopy machine.

Since many changes could be made in the embodiment of the invention as particularly described and shown herein without departing from the scope of the invention, it is intended that this embodiment be considered as exemplary and that the invention not be limited except as warranted by the following claims.

What is claimed is:

1. In an electrostatic type photocopy machine having:

a means for establishing a latent electrostatic image on the surface of a photoconductive copy sheet;

a liquid toner developing means for developing a visible image on said copy sheet from said latent image; said liquid toner developing means including a tank for containing a dielectric fluid bath containing charged printing toner particles therein; and means for guiding said copy sheet through said bath;

the improvement comprising electrode means in said tank for establishing a high intensity electrostatic field in said bath so as to plate out to'ner particles and thus reduce the concentration of toner particles in said bath; and switch control means for controlling the initiation and termination of said electrostatic field in said bath.

2. Apparatus as defined by claim 1 wherein said means for establishing said electrostatic field includes a pair of electrodes that are operatively disposed and supported in said bath, said eletcrodes when charged from a high voltage source creating said electrostatic field, whereby the toner particles in said bath are plated out on the oppositely charged electrode thereby reducing the toner concentration in said bath from an excess level to a desired printing level.

3. Apparatus as defined by claim 2 wherein said electrodes comprise a pair of metal plates.

4. In an electrostatic copying machine having:

a charging station for electrostatically charging a photoconductive member;

a means for imaging said charged photoconductive member and for producing a desired electrostatic image; and

means for developing said electrostatic image, the last mentioned means including a liquid developer tank for containing a liquid developer, said liquid developer including a dielectric fluid containing charged toner particles suspended therein;

means for immersing said photoconductive member in said tank; the improvement comprising means for establishing an electric field between a pair of electrodes disposed in said tank, one of said electrodes having a charge applied thereto that is opposite in polarity to that of said charged toner particles; and

means for controlling the charging of said one of said electrodes whereby the concentration of said toner particles may be reduced to a desired level for most efiiciently developing said electrostatic image by the plating out of a desired quantity of toner particles onto said one of said electrodes.

5. A method of controlling the toner particle concentration in a liquid developer bath of an electrostatic photocopy machine, comprising:

determining when the concentration of toner particles in said bath is too high;

applying to said bath when its said concentration is too high a strong electrostatic field between a pair of electrodes immersed therein so as to plate out some of the said toner particles and thus reduce said concentration; and

interrupting said field when said toner concentration has been reduced to the desired extent.

References Cited UNITED STATES PATENTS 2,898,279 8/1959 Metcalfe et al. 204181 3,068,115 12/ 1962 Gundlach 1l737 3,129,115 4/1964 Clark ct al. 1l8637 3,155,531 11/1964 Fauser et a1. 1l737 3,284,224 11/1966 Lehmann 11717.5

JOHN H. MACK, Primary Examiner.

A. C. PRESCOTT, Assistant Examiner.

U.S. Cl. X.R. 

